In recent years, as the performance and the efficiency of machinery equipments and power equipments have become higher, conditions in the working circumstance of lubricating oils and grease have become severer and high quality is required for lubricating oils capable of withstanding such conditions. For example, since jet engines, or gas turbines.
Gas turbine oils are top-quality rust- and oxidation-inhibited oils. In gas turbines, the lubricating oil must withstand contact with very hot surfaces, often with intermittent operation and periods of nonuse. Therefore, to be effective, the oils must have, in addition to good corrosion protection and demulsibility, outstanding resistance to oxidation, which includes a minimum tendency to form deposits in critical areas of the system.
To achieve these desired properties, it is necessary to formulate these oils and greases using a carefully balanced additive package. The nature of these fluids makes them very susceptible to contamination, particularly from other lubricants and additives. A relatively small degree of contamination can markedly affect the properties and expected service life of these lubricants. Further, to maintain effective operating conditions and to avoid damaging the equipment in which they are used, turbine oils should be kept meticulously clean and free of contaminants. Contamination is minimized by filtration of the turbine oils. To ensure that the turbine oils are substantially free of contaminants very fine filters are used.
Due to the requirements of turbine oils, only a few classes of additives, relative to other types of lubricating compositions, are combined with the base oils. Generally, finished turbine oil will contain only the base oil, antioxidants, rust inhibitors, demulsifiers, corrosion inhibitors and diluents, if necessary.
EP 0 735 128 A2 discloses extended life rust and oxidation oils comprising a dithiocarbamate and an alkylphenyl-α-naphthylamine. This reference does not teach the use of Group II or higher (i.e., Group III or Group IV) base oils, or the advantages obtained thereby, as required by the present invention.
U.S. Pat. No. 4,125,479 discloses an oxidation inhibited lubricating oil with a combination of additives comprising methylenebis(di-n-butyldithiocarbamate) and 4-methyl-2,6-ditertiary butyl phenol, said to provide enhanced oxidation inhibition.
U.S. Pat. No. 4,880,551 discloses an antioxidant composition consisting of a 1-(di(4-octylphenyl)aminomethyl)tolutriazole and at least one antioxidant selected from the group consisting essentially of methylenebis(di-n-butyldithiocarbamate); 2,6-di-t-butyl-4-sec-butylphenol; 2,6-di-t-butyl-4-methylphenol and butylated phenol mixture. International
EP 0537338 A1, discloses thermally stable lubricant and functional fluid compositions containing hydrocarbyl phosphite in combination with at least one basic alkali or alkaline earth metal salt of an acidic organic compound and a metal deactivator, the composition may additionally contain a dithiocarbamate compound for an antiwear agent. These references do not teach or suggest the combination of components claimed herein.
U.S. Pat. No. 5,856,280 discloses gas turbine lubricating oil comprising a major proportion of synthetic polyol ester based base stock including diesters and polyol esters, preferably polyol ester based base stock and a minor proportion of an antioxidant/deposit control additive, specifically a sulphur-containing carboxylic acid (SCCA) derivatives.
U.S. Pat. No. 6,191,080 discloses that addition of a polyphenyl thioether to a lubricating base oil is extremely useful for providing heat resistance and oxidation resistance under a high temperature condition.
U.S. Pat. No. 6,586,376 discloses heat resistant and oxidation resistant lubricating oil composition comprising a polyphenyl thioether as an antioxidant in lubricating oils where high heat resistance and oxidation resistance are required for lubricating oils used in jet engines, gas turbines and automobile engines such as turbo engines.
Canadian Patent CA 2196852 discloses a synthetic lubricant composition with improved oxidation resistance. The lubricating composition contains an additive formed by combining one or more polyalkylene glycols, singly or in combination, with an effective amount of one or more alkylated aromatic compounds such as alkylated naphthalene.
International publication WO 2008027883 A2 discloses a lubricating composition containing a dispersant, a corrosion inhibitor, and an antioxidant. The invention further provides a method for lubricating a mechanical device with the lubricating composition.